# Is it viable to use a Pinion gearbox system / internal gear hub / CVT gears for a road bike?

What would be the top speed if I ever sprinted using one of these?

• the top speed depends on the chainring and cog sizes you use, as well as your fitness and abilities – Paul H Sep 9 '20 at 16:29
• I think a more relevant way to phrase the question might be, how many watts (at some power output) would a gearbox cost me? If I were riding at my functional threshold power, how many mi or km/h would a gearbox cost me? – Weiwen Ng Sep 9 '20 at 18:14
• Depends what you mean by 'road bike' and for what purpose. Obviously the Pinion systems and various internal hub systems (Rolloff, Shimano Nexus/Alfine) are viable for bicycles in general and are widely used. I believe there is at least one continuously variable system (NuVinci) but I don't know how much up adoption they have. – Argenti Apparatus Sep 9 '20 at 18:18

Just a thought I had What would be the top speed if I ever sprinted using one of these?

The top speed is way over 100 km/h, probably at least 150 km/h.

The process for obtaining such unbelievably high speed is as follows:

1. You start sprinting
2. The rear hub fails to withstand the high torque
3. You fall
4. A witness calls ambulance
5. The ambulance arrives, transports you to the hospital, and this is how you obtain the >100 km/h speed

For example, Rohloff speedhub, the 14-speed internal gear hub, supports with standard sized chainring and sprocket only 250 Nm torque at the cranks.

On a road bike, in sprinting position, the handlebar allows you to obtain extra leverage. Maybe 30 kgf of extra force.

The clipless pedals allow you to pull up with the rear pedal and simultaneously push with the front pedal. Maybe 25 kgf + 25 kgf = 50 kgf of extra force.

This is added to your weight. For example, if you weigh 80 kg, it's 80 kgf of force.

So I already see 30 + 25 + 25 + 80 kgf = 160 kgf = 1569 N.

If the crank is 175mm long, this is 0.175 m * 1569 N = 275 Nm, over what the Rohloff speedhub can withstand using standard sized chainring and sprocket.

Rohloff speedhub is not the only one at fault. There are internally geared hubs that suffer from even more severe problems at lower torques, such as the Sturmey Archer 3-speed hub.

• It should be noted that Rohloff hubs do not have any safety margin past the specified limit. If you go over it, they explode immediately and violently. Fortunately the 30kg for pulling up on handlebars is completely ludicrous and pulling up 25kg is pretty close, so outside juhist's imagination one should be safe. – ojs Sep 9 '20 at 20:48